I'm sure I already posted my personal theory on this scene and how it can work with the rest of the movies overall (I'm sure it wasn't well received as I recall) but my take is this:
The Alien in this movie is still learning. Its primary instinct is to reproduce. The first two people it encounters is Brett and Dallas, and they were egg morphed. However we don't see those eggs produce a viable hugger in the movie due to Ripley's intervention. So, with the benefit of 'knowledge' from other movies (that obviously weren't conceived at the time the movie was made) let's now suppose that those eggs weren't fertile. The alien has thus far failed to reproduce. Why? Because to produce a successful ovomorph, requires something produced in the ovaries - David created his ovomorph from shaw's ovaries. What if without a queen, a female host is required to create a fertile egg?
So the Alien encounters Lambert, and is curious.. it knows she is different to the other hosts it encountered... but something is 'off'... Parker gets in the way and is disposed of -no need to trial another male. The alien "explores" Lamberts insides with the tip of its tail ( a violent and brutal rape from a humans point of view) however it doesn't find what it requires..why? Because as per Lambert's bio, she is transgender, and not biologically female. This is why Ripley is so important, and why the alien does not immediately attack in the
shuttle.it's biding it's time as Ripley is its final opportunity to reproduce.
This would also nearly tie in with H. R. Giger's art showing the xeno life cycle..a play on the Egyptian goddess nuit, the goddess of the night, where you can see an ovomorph originating from the lower stomach area of the over arching female depiction.
Again, I know this is not a well received theory, but I'm looking at this from a perspective of the alien isn't a 'species' per se at this point, this is the iteration / form the creature has taken birthed from a human host. It is new and beautiful and 'finding / discovering' itself.