Sooooo important to have strong abs/lower back before you concieve....It'll help ANYONE throughout her term!
Anyhoo...I'm not sure what kind of shape your pal is in(I'll assume she does not train at all?)..Sooo..She can do a simple squatting stretch. Have her balance/steady herself on a kitchen counter or any big piece of furniture.Sqat down and have her hold it there for a minute or so- 10 or more per day- she can raise 'em each week.Pelvic tilts are good too. Lay back on floor,knees bent, feet flat, press the small of your back against the floor while exhaling. Simple and easy.
If she trains already, I'm sure her doctor will give his blessing on a training regime while she's EL PREGO!!!
I wish her and the baby well!