Hi , I'm James DVM MRCVS and would like to help you with your question
Labradors are known as happy dogs in most cases and are easy excitable in a young age .
Her reflex of foaming comes as a result of her excitement (Some dogs foam , some wee and others can even get aggressive while actually trying to be friendly since their are so overwhelmed with joy that their body can not deal with the surge of Adrenaline and other substances which affect the nervous system)
Is it possible Bella is having a season currently and is coming in contact with entire males ? (this could cause her to get very excited as well)
In answer to your question - spaying her will not change her natural excitement to see other dogs .
But training might help her restrain herself better when getting in contact with other dogs as well as age will do it's part as she gets older she will becalm calmer .
I would not suggest and drugs to treat this natural behavior !
I hope this helps
I you have any questions please let me know .
all the best
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hi again. I wanted to know what have you decided about Bella