I came back fom maternity leave pregnant which wasn't exactly planned. It was a really large company and I had only been off for 4 and half months so hadn't used my full maternity leave provision, I also then worked up to 1 week before my due date despite them attempting to make me redundant whilst about go off. I argued against this as I fully intended coming back after a similar break and the first stage of the redundancy process was to allow you to try to find an alternative job within the company, I felt at a disadvantage in interviews with my stomach sticking out like I'd stolen a medicine ball and hidden under my top! They then agreed that my notice would start as soon as I returned. I returned after 5 months worked 4 months notice and they made me redundant. I had worked for the company for 8 years before becoming pregnant. Despite having been in a similar situation to your friend, it depends on her circumstances and attitude as to whether she is taking the pee. I had all intentions of returning to do my job and had very short periods of mat leave. My husband stayed at home and looked after the kids, so I was a reliable employee. I got a job a couple of months after being made redundant and had temp-ed during the gap. I still work for the same company almost 9 years later and have had a bout 3 sick days.
What I am saying here is that it really depends on your friends future intentions and previous record with the firm. If she has been a hardworking loyal employee, has taken a moderate amount of mat leave, intends to do the same this time and also considers that her family will be complete and has adequate childcare in place to ensure that she is not running off every 5 minutes then i think she should explain this to her boss and judge his reaction. If on the other hand she intends to maximise her leave and return part time or not at all and her heart isn't in the job, then I think she should resign.