I’ve the previous version (105 bhp 1.2 TSI) in a Roomster.
I had doubts about a 105 petrol after a 105 (1.9) TDI before buying but not found them founded (well, other than trying to get up the Lecht from Corgarff, I had to drop into 2nd at the steepest. But it’s a 20% incline, and coming from diesel I’d let the revs drop…).
If anything I think the 105 might verge on a bit too ‘lively’ in the Roomster if you really give it some. For your mum (is she 60-ish/+?), I would have thought the 90 realistically would be enough. Unless she lives for speed…