[Pebbles]

That is unusual.

Biologically speaking there are two main hormones involved in inducing lactation. One is progesterone and the other is oxytocin.

Progesterone is responsible for the synthesis of milk from the milk glands, Although it doesn't do it directly what actually induces the milk glands to produce milk is a gradual decline of progesterone levels from an initial high level to a much lower level.
This typically occurs after pregnancy although any number of effects can induce it not all of which are harmful.

Oxytocin however... This is the actual hormone that squeezes the interior of the nipple and causes milk to come out, without this you can't really lactate like that girl was... Also another random point Oxytocin is used to stimulate other involuntary contractions such a birthing contractions. Oxytocin begin produced inappropriately can be a sign that something is seriously wrong. Given that it's released from the hypothalamus.

So in her case... I dunno either she's recently given birth... Or she's taken some very strange medication... It's of course possible that she's just a freak who has that response from an orgasm

I've heard in medical literature of people having numerous strange problems upon having an orgasm. From loosing feeling in there extremities to extreme pain. To other more bizzare things.