I appreciate all this is "possible" but she does very few ads in her posts. Maybe some more in stories which command less ££. Gift products aren't income, unless she resells them (for less value).
Most big brands wouldn't just look at her following. If your engagement rate isn't great and there is fear of "bots", I can guarantee you they will not work with you.
I worked in Marketing for one of the largest sports brand and we only paid actual cash to very large celebrities and influencers with 1M+ following, the rest would just get free products.
Regardless, unless she is lying to the same government she works for, if you look at her company accounts for the past year, her revenue is only around 20k. The year before was just over £4k. Hardly the big bucks she claims. You have to consider she will have to pay tax on top (and include her salary as revenue) so if you do the math, that does not add to £2k a month. She is also claiming no expenses, but realistically, she may have had to invest in lenses, cameras etc for the business. It'd be very silly not to claim it from a tax perspective. If I was her, I would be putting things like my car and anything that could potentially be claimed as a "business expense" through the business to get a tax relief.
EDIT: She will also have to pay the accountants, which is clear she uses from her company address. A standard business expense.
So either she is lying or she is taking cash home without formally reporting in her accounts (nor paying taxes).
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Definitely not that amount from big brands. I know this first hand. Also she does few ads on posts. Also, this isn't showing in her company accounts. The reason why only small-ish brands work with her is because these are less likely to consider engagement rates.