We're not allowed to diagnose, so you should really contact your GP /hospital team for more help with what may be going on. I've certainly experienced ankle swelling when in hot climates, long time sitting or driving, sunburn, insect bite reactions, etc. When I first went on insulin (MDI) 16 years ago I had been chronically dehydrated, so my lower legs swelled very dramatically, but fortunately my circulation, kidneys, etc then stabilised quite quickly so I haven't attributed any subsequent swelling episodes to insulin.
Did you change insulins when you started pumping? Where do you wear your insulin pump? At least in my experience it seems quite unlikely that a hormone (i.e., insulin) response would affect one leg only. But other conditions could be involved, so I do suggest you follow up with your GP, not just the diabetes team.