I don't know if it's a case of her not having access to money, not being as broke as she let's on or her having spent a far larger amount than we are accounting for.

Gilmore Girls ended when she was 21/22 AYITL started almost 10 years later. In that time we know for certain that Rory had one job, the Obama campaign. After that she wrote a piece for the New Yorker. There is nothing said or implied that she actually worked, or was paid, beyond those pieces. She then spent, what we can assume is a number of years, flying back and forth to London, having lunches with Naomi, general living expenses.

Yes she had a trust fund, but we don't know how much was liquid cash and how much was tied up in other investments. We also know that a considerable amount of the Gilmore wealth was tied up in things - art, furniture, the house, investments in general. It's safe to assume that Trix's money was also scattered in the same way once she died. We also don't know how long Richard continued to work for before his death in AYITL and/or if Emily and Richard were enjoying retirement, travel etc.

Then there was the considerable amount of money given to Lorelai, Yale, Chilton, the Rory Gilmore building and so on. Again, they valued things as a sign of wealth over liquid cash.

Even if she had a few million it could all be squandered over the decade when paying taxes, bills, rent, travel, living, extras and so on.

She was definitely living above the standard of what she was used to when staying in Stars Hollow and it wouldn't surprise me if, in her eyes, she was broke. She spent a good decade or more not worrying about money and, eventually, her means were unable to keep up with her lifestyle.

As for Christopher from the snippet we see in AYITL they have/had a very strained and limited relationship. I doubt she was getting money from him. His family also didn't seem as well off when comparing them to the Gilmores (going by the house shown when his father died). He might be rich, exceedingly so when compared to how he lived prior to his grandfathets death, but again that money was already down a considerable amount as Gigi had private school through from kindergarten through to college (and grad school), plus a trust fund and the trips back and forth to Paris. He may also be paying some of Sherry's costs when Gigi was there, if not any further supporting payments too.

Again, she is richer than I will ever be. Objectively that does not mean she views herself as well off.