why not if she's paying for it and your dp can't go. Personally I've never been one for involving my mum in the scans/birth but in your instance if you really cannot find a day dp can go with you then it's nice for you to have someone there to share it with esp if she's also paying anyway.
My hubby and i had one paid for as a leaving presie from my office. We had my mum and brother and hubbies sister. It was so special to share the 'baby preview' with all of them. I bet your mum would love to be able to share the experience with you. It is quite special because you are literally looking at your baby, you can see everything! I found it all a little overwhelming and loved having my family there to share it with me. Trust me all eyes will be glued to that screen, no one will notice your stretch marks!! Enjoy....xxx
Let her go with you if your partner is away. I met up with my parents for my 4d scan with dd2 as it was nearer to their house and also when I was pregnant with dd1 we wern't in contact. The only problem was that my Dad and I wanted to know the sex and Mum didn't. It was just as well Dad and I were well practiced at keeping secrets from mum.