There are HC viewing areas for fireworks -- just ask CMs ahead of time so you'll know where to go. Also, the current fireworks show is designed to look a bit different from different areas: the castle, Main Street, ROA, and IASW. If you view on different nights, you can view from different areas to get new perspectives on the show. If you view from Main Street, try to be up at the rope by a crosswalk so that there won't be anyone directly in front of your daughter's wheelchair.
You can see the fireworks from DCA (we watch from BVS), but there isn't an official fireworks show there. The night shows there are WOC and PTN. WOC has a HC viewing area -- ask the CMs where to go. PTN has a very long parade route. You should be able to find front row viewing somewhere along the route with about an hour (maybe a bit more) wait.