Oh, and she may also have had her mother do this to her. A friend had her step-mother do it - she was allowed 3 friends at her own wedding, while her stepmother asked 20. I think it used to be the norm and not all mothers have acclimatised to weddings now being planned by the brides, and not their mothers.
There was a mother on Mumsnet a few years ago, genuinely indignant that her daughter wanted a wedding in the way she, the bride, wanted and liked it. The mother posted, fully expecting Mumsnet to side with her - was so shocked to have her backside handed over instead. She said that the invitation comes from the parents of the bride, and the bride and groom are honoured guests, and therefore the planning is done by the mother, with input by the bride, as the mother and father are paying.
When it was gently explained that that isn't how things are done now and that the bride and groom choose their own wedding, and host it, not the bride's parents, she sniffily said no wonder brides are so Bridezilla and selfish these days. She clearly, and honestly, expected to run the wedding exactly as she wanted, and assumed that given it's traditional for parents to pay, then it's obviously also correct that they call the shots. (I seem too remember that she was proud that they'd declined the suggestion that the bride and groom pay, too! Often wondered what happened in the end with that one.)
She sounded awful, as a parent, but I felt for her a bit - she'd had her mother take over and glory in hosting her own wedding, but now it was her turn, her daughter was refusing to let her have her own day in the sun hosting, and make all the decisions on the day. So your mum may still be of the view that her mum planned her wedding, and now it's her turn to plan yours - in which case she's being quite relaxed in just asking for (impossible) friends to come. Either way, sitting down and working out what the expectations on her side are is imperative, or the day will be soured.
And for the love of God: if your only invited friends are two bridesmaids and the best man, ask at least the final 3 spaced as your friends, and not your mum's. Or it's going to be like wearing a wedding dress at a family Christmas.
Apart from anything else, what about your fiancé's family? Does his mum not get to ask 14 people, too?