Constipation and full fat milk

So we switched over to full fat milk from formula at 1 years as advised.

Since then my daughter who is now almost 15 months has had issues with constipation. When she gets constipated we mix it with semi skimmed milk and after a few days her poop returns to normal and then we introduce more of the full fat milk and she gets constipated again. 😔

Now she is becoming uncomfortable and starting to refuse solids.

Anybody else experience this or have any recommendations?

I asked the health advisor and she just said carry on with it and make sure she's eating a well balanced diet and gave me a lecture on baby led weaning. We did baby led weaning since she was 8 months and only recently she has had an issue with food.

She also advised to give less milk and water as she is being full up on it.. she only has 8oz in the morning and 8oz at night. And I thought water would help the constipation?

She's always been rather petite and on the lower percentiles so I'm a bit concerned