Difficult. It’s hard to believe that someone in DMR for 15 years would have such a rapid molecular relapse within 3 months.
To answer the question, she is very likely to lose CCyR and CHR, but hard to know how quickly this will happen. Ideally she should return to a TKI, perhaps one more potent than imatinib, re-establish her deep response and try again in a couple of years.
If she is adamant that she will not re-start I would suggest another 3 months off drug. If pregnant by that time, do nothing and just monitor counts and PCR. Try to get to the 3rd trimester before starting any treatment and if necessary, at that time, try imatinib. If she needs treatment before then maybe seek advice according to rate of rise of PCR
If not pregnant, I would recommend re-starting a TKI. If they have access to an IVF unit, refer her because any further attempt could be speeded up with fresh or frozen embryos. If she won’t re-start then she must understand that she is at risk of disease progression.