She must have thought side slits looked more fashionable

Seriously though, it is well worthwhile having this kilt professionally repaired when it is so precious to you. I have a cheap acrylic kilt which I like for casual wear and it got ripped when it caught on a drawer handle and I repaired it with a few crude stitches so that I could continue to wear it around the house and out to the shops. However if anything similar happened to one of my quality kilts I would be only too happy to pay someone to do a good repair job.

Perhaps you should cut your daughter's pocket money to pay for the repair.