So-called "BRSS" is completely discredited pseudoscience whose sole purpose is to push a homophobic, misogynist agenda. The entire premise behind it is absurd.
And no, there's simply no realistic mechanism for hormone transfer (in significant amounts) through bodily fluids, which is why there's no research on it. Trans, cis, it doesn't matter, your blood/fluid concentrations of sex hormones are so low as to be completely meaningless for your partner.
A trans guy injects/applies on the order of (not giving a specific dose) 100-250 mg of testosterone esters each month. Call it 250mg. The average guy weighs around 75kg = 75,000 g, at about 80% fluid, so the average guy has about 60,000 g = 60,000 ml fluid in his body. If all of the T that the trans guy takes in an entire month were present at one time in ester form and evenly distributed throughout his bodily fluids (this is not the case, so I'm overestimating the concentration) then the concentration of T esters in his bodily fluids would be 250mg/60,000ml = 0.004 mg/ml. That's just not going to add up to a significant dose on any sort of relevant time scale. And I'm being extremely overgenerous about the possible concentration.
If there is hormone transfer between a trans guy using testosterone gel and his partner, the gel is the culprit. Even a tiny amount of gel residue soaking through clothes or being picked up from clothes/sheets is going to deliver a dramatically higher dose than whatever miniscule amount of sex hormone may be present in bodily fluids.
Of course, it's also possible that the partner's high T levels are endogenous. The way to find out is by eliminating the gel as a possible source, by going on injectable T or avoiding physical contact and bed-sharing for a few weeks, and testing her T levels again.
