The 1242 Mabel who was the widow of Harvey de Stafford, who was also mentioned in the post of Chris Phillips BTW, could indeed be another generation, or indeed someone who remarried. And she could have remarried more than once.
The proposal that she at least re-married to Robert de Lisle is taken up by CP (under Lisle), and Richardson (RA, Vol.3, 581). Richardson says Mabel and Harvey had no issue. I presume this is based on the fact that Harvey's heir was his brother Robert. However, in the 2003 discussion on this newsgroup Jim Weber raised the question of whether we really should assume that this was one Mabel. "It doesn't make sense for a woman to marry as a 2nd husband, a man who might not have quite been born when her 1st husband died."
Let's play devil's advocate. Could she have married three times? Could she also be the wife of Geoffrey d'Amblie? In that case she married him around 1245 which is after 1242 (when we know Harvey was dead) and before 1252 (when we know Mabel was married to Robert de Lisle).
Concerning the 1252 Isabella de Aumbley, as far as I can tell it is not specified that she is the wife of Geoffrey, although I think she has to be part of his family because Geoffrey had been holding Norton. (Cold Norton in Essex was one of the manors John de Bathonia later held by right of his wife, the daughter of Geoffrey.) But could Isabella have been a widow from another generation, for example Geoffrey's mother, or step mother, or grandmother? Could it be that Mabel the wife of Robert de Lisle in 1252 was actually also the widow of Geoffrey? We do not have an exact death date for Geoffrey, but it may well be before 1252 as far as I can see so far.
In 2003 Chris Phillips proposed that Isabella was Mabel's sister. He also suggested that alternative explanations might exist for why the wife of Robert de Lisle would be specially favoured in the will of a d'Aumblie widow. Is one such possibility that Isabella was Mabel's mother-in-law? There is one obvious problem, and this concerns the byname given to Mabel in 1255. Bynames were not necessarily fixed, especially when women were being mentioned in relation to specific lands connected to a specific family. Nevertheless it is a problem for this proposal that the 1252 Close Roll entry tells us of a Mabel who was already married to Robert de Lisle in 1252, while the 1255 entry mentions a Mabel de Aumbley.
Still, something is going on: The 1252 already connects Mabel the wife of Robert de Lisle to the family of Geoffrey de Aumbly who married a daughter of Robert de Muscegros in 1245. The 1255 entry specifies that Mabel DE AUMBLEY living at that time was a daughter of Robert de Muscegros. Another 1271 record cited by Phillips and CP states that Mabel the wife of Robert de Lisle was a daughter of Robert de Muscegros. (Is it necessary to propose multiple marriages between the same families, and multiple people with the same name?)
Irrespective of all this, it still seems unlikely that Eleanor the wife of John de Bathonia was a granddaughter of Robert de Muscegros. The problem is still that we know that the Amblie-Muscegros marriage happened in 1245. Geoffrey de Amblie's daughter Eleanor was married and granted free warren in 1257. Her own daughter Joan was 25-30 in 1291 when John de Bathonia died indicating that Eleanor was of child-bearing age in the period 1260-1265. These rough dates seem to make it unlikely that she was born after 1245. So Eleanor may have been the daughter of an earlier wife? I hope others will check my thinking.
I am also still wondering about lands. In the case of Mabel she can also be connected to the Muscegros family because of her involvement in Kemarton (Glo.) and Finsborough (Suf), which she swapped with her brother. Did the Amblie-Bathonia-Bohun inheritance include any Malet or Muscegros lands? I don't see any. Here are the IPMs of Robert de Muscegros
https://www.british-history.ac.uk/inquis-post-mortem/vol1/pp80-86 and John de Bathonia
https://www.british-history.ac.uk/inquis-post-mortem/vol2/pp486-498 . If Eleanor was the daughter of Mabel then we can understand that Mabel had a male heir who received her inheritance. If she had another Muscegros mother then we know of no other heirs and so it seems her mother did not get a fair share. Perhaps simpler to suggest that Eleanor was not a descendent of the Muscegros family.