What happens if you are away from her for more than a couple of hours? Is there the option to have someone else feed her solids and not have the boob there as an immediate option to see if she takes a little more?
While I would never advocate starving a kiddie we found that if I tried to stretch DD out a bit (finding the happy medium between making her wait a while and sending her into a total meltdown) then she was happier to eat more solids because she was actually genuinely hungry rather than just a little peckish.
Maybe if she is still just snacking you could add higher calorie foods like avacado or baked beans (I make my own - but the salt reduced ones are OK too)
In the end I work on the theory that if they are happy and active and engaged it will all be OK

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