Underground Aquarium

You've illustrated your story of a lost princess remarkably well here though rather than the cave being the source of focus here, it seems to have got lost amidst all the details and colours which is making it hard to tell what is important and what is not.

And the cave rather than you wanting it to look like a doorway to another magical underwater is merely looking like a hole pasted on the wall. You should work some more on blending of the cave to match it with the rest of the environment, now it stands out too much. I'd recommend to add color reflections from the nearby stones and adjust the perspective a bit.
Also work on the transparency of the water (especially near the borders), stone has width and we should be able to see it from this perspective.

The other thing that bothered me is despite it not being an overdone piece with regards to details, the environment in this scene still looks a bit busy because of the bubbles and the fishes placed all clustered together.
With the bubbles you could have either added few or placed some as enlarged in the foreground with gaussian blur to get a lovely DOF but they certainly are a beautiful addition in the scene.

As for the fishes by placing them apart perhaps one or two to the left, in front and behind the model would have lent a balanced focus and alignment to this piece.

Coming to the model now, her clean dress sort of bothered me. Since you've shown as a Princess lost on her way home, it is obvious to imagine that she has travelled much to make her dress slightly dirty (even though it is a fantasy piece, one has to still incorporate a touch of realism).
Maybe using a mossy/muddy texture on low opacity on multiply mode will work to make the dress appear dirty, especially the lower part.

Next, the flame torch's light bouncing on the wall makes me wonder if you've not put the layer on color burn/color dodge mode? If so, the best way to paint light reflected on any surface/object, it is always wise to go subtly (low opacity of the brush) by building up the lighting using various shades of orange or yellow. Remember, one colour itself will never give you a productive result with lighting.

You have submerged and blended her lower dress in the water quite nicely but there should've been shadows around it.

Overall, the colours here really complement each other and not overdone at all. The model and her expressions - that of curiosity yet delighted at discovering a magical aquarium is perfect too - great choice on the model dear.

Being a witness to your artworks from the very beginning, I must commend you of making massive improvements in your creations. You love playing around with the colours and magical effects and in such a short while have accomplished much.
I advice you to keep working & developing your art style, try getting out of your comfort zone. Though you've done arts of several different themes, make sure to understand that same colour scheme always will not work with every style and mood of art.

With a powerful imagination & sense of creativity you can go a long way ahead if you put in greater efforts. Keep it up!

Thank you for reading this, I hope you'll like my very first critique.