Surely if you're a Penelope of any flavour, you absolutely must have a pony.
I don't know about my cousin, but my pal Penelope had a much, much bigger horse. Hunter-thoroughbred cross, which sounds impressive. No idea how many hands*, but it had 4 hooves. It was about 5' 8", or head height for her, at the withers, so she told me. I'm not sure what a wither is. If the Lord be withers...
*My friendly horse conversion chart tells me 17. Do they do metric horses?