Second, in general a "high-end escort" is very unlikely to have HIV, or other transmissible STDs, partly for exactly the same reasons your partner gave you:  most understand the risks, care about their health, and take precautions to protect it. In addition, probably the large majority of their clients are at low risk -- that is, you probably are a typical client. Even among the highest risk female sex workers, fewer than 1% are infected and I would judge the chance your partner had HIV as under one in several thousand, especially if she is telling the truth about recent negative testing. (And few people lie about HIV status when asked directly.)

The average risk of HIV from insertive anal sex, if the receptive partner is infected, is estimated by CDC to be 1 in 909 -- you can round that up to 1 in a thousand. For only 1-3 seconds of unprotected exposure, it's undoubtly lower still. So if we guess your partner had 1 in 1,000 chance of HIV (probably too high, but let's go with it) and 1 in 1,000 chance of transmission, your HIV risk was something like 1 in a million (0.001 x 0.001 = 0.000001). And lower still because of the brief exposure, so more likely only one chance in several million.

So your risk too low to be tested on account of this particular event. Of course you are free to do that if you believe you would be further reassured by the negative result. Alternatively, ask her to be retested (and maybe pay for it) -- if she is negative at this time, you can be even more confident you were not exposed. In addition, everyone who is sexually active outside a committed monogamous relationship should be tested for HIV from time to time, like once a year. If you haven't been tested recently, maybe this is a good time, since it's on your mind. But not because of these particular exposures.

I hope that helps. Let me know if anything isn't clear.