Re: Dropped to 25th percentile :(
I wouldn't be too concerned. Both my kids dropped considerably in percentages after they were born. There are a lot of factors that can inflate birth weight and if you feel baby is happy, healthy, meeting milestones, things are probably just fine. Of course, it's always a good idea to keep an eye on things to make sure when there is any doubt. Since dirty diapers are so variable, it's best to count wet diapers. If you're getting 5-6 per day, your baby is getting plenty to eat.
It strikes me as odd that your HV would recommend a bottle of formula. Even if there was a problem, what good is a single bottle of formula going to do? If weight gain truly is a concern, there are many things you can do that don't involve supplementation. Here is an article that outlines a few of them.
Judging by the HV comment about hindmilk, I suspect she doesn't actually understand how breastfeeding works. There are typically signs if a baby is getting too much foremilk- green foamy poops, gassiness, excessive fussiness. But if you feel feedings might not be lasting long enough you could try changing positions or switching sides more often while nursing to encourage baby to stay awake. Or try some breast compressions while baby is still latched on- if the milk starts flowing again she'll probably start swallowing. If nothing else, just try offering the breast more often, even if she isn't acting hungry.
There is definitely no need to introduce formula at this time. Doing so would only hurt your milk supply and potentially give your baby nipple confusion.
“We are not put on earth for ourselves, but are placed here for each other. If you are there always for others, then in time of need, someone will be there for you.”