(1) Yes, if your married sister is poor and not sahib-e-nisab then you may give her zakah.
() If the said woman owns some cash along with 7.5 tola gold though only one rupee and the total cost of gold and cash reaches equal to the cost of 613 gram 360 milligram silver then zakah shall be fardh on her whether she uses the gold occasionally. It is not necessary for zakah to be fardh that the gold is in use.
Allah knows Best!
Darul Uloom Deoband