I would add emphasis on the SLP who works with AAC. Here in CO, SLPs either work on verbal or AAC but generally not both. (In the schools, you have an AAC state level team that trains the local SLP / aides / teachers but the SLP is verbal based.) While teaching strategies may be the same, knowledge of the device and device specific issues are better suited (IMHO) to a SLP with AAC experience. I would add that you want to consider both immediate communication and long term communication and lots of apps and devices work well for immediate needs but have no growth path for long term, independent communication. Will Touch Chat be understandable by your daughter, your family and her providers now and will she be able to grow with it in the future for independent communication? Do you all model with the device, ask her questions using the device only? If she is hitting random keys, do you take the device out of reach, respond to the statement made and then give her back the device so that she understands her words have meaning and create interactions?
For you, as you have a little bit of time before summer, I would suggest:
a. Can you identify specifically what you'd like to work on over the summer, greetings, requesting certain family members, food items, etc...
b. Once you have identified a short list of summer goals, think through the best approach for the app, ie., hide all icons but those, leave all icons but color code those, create "cheat sheets" that show the sequence, etc...
c. Then, make sure everyone is at home is educated, i.e., everyone says "hello" and waits for your daughter to say "hello" back. If she is having problems, the person models the method to say hello and tries again. Then shows the cheat sheet if needed. It is hard to break habits, i.e., to allow your daughter to express herself without the device.
d. See if you can have in home therapy from an SLP - AAC over the summer. This person can really help you identify real life scenarios for practice based upon your home routines and goals.
e. You might consider an IEE for an outside evaluation of AAC devices, i.e., an evaluation with a seating specialist, access / OT specialist, vision, autism and SLP. There are lots of apps / devices and there may be one that is better suited to your child. (I believe that Autismate is endorsed by Children's Hospital Boston - one of the top SLP AAC places for kids.) You may want to talk with an advocate or attorney however as there are steps to follow for this process. If you have an assessment, I would strongly promote that you make a list of things you want in the hardware and software, i.e., portable, loud enough for people to hear (without speakers), vision considerations (size/color/shape of icons, other low vision enhancements), a stand, wheelchair access (if app), durability, warranty, access method needed, vocabulary (icon, phrase, visual scenes, literate, not literate, both, etc...) training / growth paths, training support, amount of customization required, etc... CO has a loan bank so that you can trial devices for longer than a demo and/or have access to the device while waiting for the insurance/Medicaid funding to go through for the selected device.
f. If your state has ABA coverage, I would HIGHLY recommend having an ABA person / team help you over the summer. They can create a rewarding program for your daughter where they master icons. They can help show you how to use the ABA method when they are not there, i.e., how to be clear in your communication, how to provide positive reinforcement, how to track data to see if you are making progress, etc...
In essence, you might, depending on your insurance/Medicaid waiver, be able to create a functional summer school program at home to focus on figuring out how your daughter learns, what motivates her to use her device, what the best device / program for her will be, etc...
We have never used TouchChat. (My son is 13, has multiple challenges - legally blind, triplegic CP, nonverbal, seizures, etc..) I found it frustrating, i.e., pronouns in different locations, conjugations spelled wrong, no icon search (to help you find an icon), the requirement for literacy beyond a low level of icons, four hits for the word "water" etc... We use PRC because they have LAMP (language acquisition through motor planning) and a very streamlined icon location system and icon search help. I also picked it, because, as an IT person, I did not want to be building pages and/or redesigning his device every few years. (I'm not trying to change your mind. Just explaining why we do not have it.)
We have always programmed our son's device so we are not having to wait on others. Because of Robin, the AAC Institute and attending Closing the Gap, I have been able to be a much stronger and better advocate for his needs.