It depends on what her motivations are, doesn't it?
I knew someone in a similar situation who retired and moved back to their country of origin without giving up their U.S. citizenship (the motivation for the relocation had nothing to do with taxation). They came back after about a year and a half because they felt their Medicare plan (i.e., taxpayer-funded in the U.S. was much better than what they would get in their home country.
Do you think I like THAT in a person?
Anyway and to the point of your query; It depends on what her motivations are, doesn't it?
I know her and you do not so you can only guess and I know (in this specific case!) She was proud and happy living here in the US, she lost her husband and went to visit her old family in England, she fell and broke her hip and has become an invalid at an advanced age. Does that sound like a deliberate plan to you?
She would be very happy to retain her US Citizenship but through a new and complex governmental reporting requirement, she now has to give up a treasured status. She is what some would call 'collateral damage' in that she is an innocent bystander that the IRS & Congress steamroller runs over to get to the 'Swiss bank accounts' of the wealthy.