the words heart condition and stumbling are never good so yes, if there's a suspected heart condition and she is wetting herself and/or stumbling, i say definitely ER.
with my little heart baby, the cardiologist told me that if he ever couldn't walk, ER right away
edited to add: i don't think the lasix messes with the diabetes so much as if there's a heart problem, if she's uncomfortable, the BG's would rise from the uncomfortable-ness