Thank you for your replies everyone.
As for those who think I'm judging my mum's intentions, I think you have misjudged mine. I didn't want my mother to do this for her own good and you can see from Sr. Gossamer's and Sr. Cat's posts that it isn't good to flaunt your good deeds. I knew she'd be hurt no matter how gently I told her. I hoped Allah would provide me with an answer as I didn't want to ruin her itkaaf or her mood. At the end I felt I should ring the mosque and ask for their opinion. I was met by an answering machine as the office was closed. Alhumdulillah, there wasn't going to be an announcement and I didn't have to give my mum the news that would've upset her. I just told her I rang the mosque but their office was closed until after maghrib. I took flower garlands and fresh flowers to welcome her out of itkaaf with the whole family and a traditional dress and jewellery as eid prezzies for her. She was very happy. Allah had saved the day.