My mum has fibroids is there any point in trying to lose weight?

she wants to know if she can do abdominable exercises

Yes, she can still do abdominal exercises. She'll just have to work harder at losing in the midsection than most people.

My mum had the same problem and was operated on 2 years ago. She struggled with exercise too, and has lost a bit of weight but not enough. She is 62 and enjoys life, so what can you say? It is up to the individual.
you can diet if overweight but fibroids wont go away with exercise if they are large only an operation would do the trick
If your Mum has fibroids it is likely she will need surgery to be rid of them.
If she can manage the exercises without too much pain or discomfort then it's OK. If she needs to lose weight then it will help the surgical procedure if she does so prior to the operation.
I don't know how old your Mum is but fibroids do shrink with age and cause no problem.
Weight is another matter. Exercise is good.