It is so weird isn't it? Especially as Echo said, if everyone did this she wouldn't have her job!!
I have seen the blog post about alterations before and am quite aware of how important they are. I have hardly ever paid for them. I do my own hemming, and can manage to take in seams. But I would hesitate to work on a jacket (Deborah, what sort of alteration did you make to yours?)
The only solution I can think to understand her (short of asking her, which I'll do next time I am up there) is that she may think alterations are for well off people, which I am not. Labour costs are higher here, and many of her clients are pretty wealthy and have bought expensive items online or on sale and so can factor in an alteration cost.
But, as my Mum was arguing when I was trying to suggest to her that she buys things and then gets them altered altered, you can end up paying as much as for the item itself! This does influence my thinking (which is why it would have been great to have my SIL's advice before I bought something!)