My mother has been struggling with her weight since she was about 35ish (after she had me

) and she's been inspried by my success lately and wants to finally loose the weight and maintain.
She's been on weight watchers, lost about 20 lbs and regained, she's been on the Suzanne Summers diet, lost about 20 lbs and regained etc etc.
She went through chemo-therapy for breast cancer almost two years ago now, and swore that when she was all back to normal (as normal as could be), she would work really hard to lose her weight. She's asked me for help with calorie counting and such.
She's currently 5'4, 196 lbs, and 56 (this coming Thursday).
From this I've calculated (hopefully correclty) her BMR at roughly 1550 calories a day to maintain.
She currently goes to deep water workout twice a week, says she will go to the gym twice a week for some cardio, does yoga at least once a week, and goes for walks with my dad most evenings (about 45 minutes at a brisk pace), so she is fairly active.
I've trying to figure out how many calories for her to eat a day for weightloss. I'm having problems with my guestimating though, and I don't want to give her a number that is too low, or too high.
At a loss of 1 lb for week, so 3500 calories, I thought 800 for the deep water workouts, 600 for the gym visits, plus cutting 300 cals per day out of her diet would give her about 1250 calories per day.
How does this sound? Too little? I know she does Yoga and walks as well, and that I have no clue how many calories are burned from deep water workouts.
Any suggestions for me (and her?). I've told her about a lot of tips in the starting off thread.
I also think she would be happier with say 1.5 or 2 lbs a week loss (wouldn't we all?), but I want to make sure she does this completely healthy.
Help!
Edit: Oops, forgot. Her goal weight is 150 lbs (for now)