It's possible, but then again, it might not be... Your HV can actually see your baby (unlike us), and she knows you and your baby, so I think it is worth listening to her.
What do you mean by 'loose poos'? Almost every ebf baby has fairly loose poos compared to the neat little sausages produced by many formula-fed babies?
If your baby is bringing up vast quanitities of her feeds, this may be reflux rather than cow's milk intolerance. (I feel weird even suggesting this, as lots of mums have problems with cow's milk intolerance/allergy being diagnosed as reflux - but it's just possible that in your case it is the other way around).
It might even be that you just have a huge let-down of milk which is overwhelming your baby.
Is your baby gaining weight? Is she otherwise healthy? Does she have any eczema, or sniffles, or crying episodes beyond what is 'normal'? Is there any mucous or stringy bits in her nappy?
SO many things are possible. How do you feel about going with your HV's advice, keeping a food diary and seeing what happens?
Let us know how you get on, whatever you decide.