Is there a single word that refers to a vagina secreting lubricant in response to sexual arousal?

There is no physiological term for this phenomenon. If you don't believe me, please read this.

Salivation is an active process, as is lacrimation. Rhinorrhea (a runny nose) has no active verb either; the nose isn't mucorating, rhinorunning, or anything else. There is excess mucous production and gravity does the rest.

Similarly, the vasodilation and subsequent transudation of fluids in the vagina has no active verb. Nor does the tumescence of the penis (it's not "erecting".)**

There are slang words for these processes, but they are not akin to "salivation."

There aren't single words for everything under the sun.

Edited to add I was wrong. Tumesce is a verb. HT to @Frank.

Elsa was horny and became wet

If you can change the verb to "became", then this is probably the most 'tasteful' way to specify female sexual arousal in this sense. The first adjective eliminates any ambiguity.

I feel it is the most widely used present-day expression, found in almost all mediums - from novels to film. Given the presented sentence structures and limited context, I believe this may be more in line with what you are looking for.