It depends on the location.
Now answer to this:
Tsunade vs Gaara
Location: A closed area. ( so Gaara can use only his own sand )
putting them in a closed area actually nerfs tsunade as well,cuz then she wont be able to summon katsuya,cuz that summon is easily taller than trees and even the hokage building,so if she summons katsuya,she will make a hole in the wall.allowing gaara to acquire more sand instantly.
Tsunade vs gaara,tsunade is a taijutsu user,she needs to
get close to him to hurt him,
"Orochimaru coveted this ability greatly, stating the kekkei genkai granted the user an impenetrable skeletal frame, which can resist any type of physical attack. In addition,should a Shikotsumyaku user ever go on the offensive, they could instantly turn their bones into the sharpest spear. Overall, the Shikotsumyaku is considered to be the
ultimate taijutsu ability, which is held in high regard."
gaara was using only his gourd sand to hold back kimi,whose speed was a 4.5 and taijutsu was a 5,when he was 13,currently his sands have gotten much faster and stronger. He carries a shitload of sand in that gourd,the gourd itself is sand as well. If she punches the sand,it will just break down,and gaara can use it to grab her and do a sand burial. He could fool her with a sand clone,he did it in the second it took for lee to blink at 12.
Honestly,taijutsu fighters are just not fit for facing gaara,even guy and lee both agreed that taijutsu is useless to gaara. If it were outide,and gaara could use only his gourd sand,then tsunade would take it mid diff,cuz she can use katsuya.
Oh and what stops gaara from er...destroying the surroundings of the closed space to make more sand?,his auto defence would save him from any falling debrisxd