I imagine she suffers from bladder incontinence, I have this due to a prolapse, can be very embarrassing, have discovered incontinence pads and knickers and change underwear more than once a day.
You really do need to have a word, I realised it myself and took steps to deal with it but she may be unaware of the odour. Others may not be as kind. And without probing try to find out if she has bladder incontinence, assure her that this is common and recommend pads and knickers if you feel you are close enough to say these things.
All the best x
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