Honestly Mac, I think she believes you can't love or bond with more than one horse at a time, so feels sorry for horses whose owners have more than one. Nothing could be farther from the truth. It's like having children; you don't love a second one less, your heart expands to love each one of them in their own right.
When I only had one child, I wondered how I could possibly love another the same way. I have five now and you are absolutely right; your heart expands. It's pretty cool how the heart works like that.