Today, a little girl, who looked like she had chicken pox, stood about 4-5 feet from my 5m old daughter for about 2 min. how likely is she to get it?

Unlikely: no set up for infection and we don't whether the other girl truly had chicken pox? in addition your 5 month old baby has got enough passive immunity from you during pregnancy till age 6 mon,

Possible/unlikely: Even brief exposure in close proximity could pass this potentially airborne germ. However, unless you never had Cpx as a kid, you passed enough immunity to baby during pregnancy to protect her. The incubation period is 10-21 days with peak eruption at day 14. When an infant has Cpx at that age it is usually mild.Newborns and adults are not so lucky.