High TLC rule out the possibility of corona virus General weakness is due to dehydration & electrolyte imbalance , which is the reason of low BP also . It normally happens if any fever last for 1 week & u do'nt take oral liquids well.she might be having some vit( D3 &/or B12) deficiencies also So start giving her plenty of oral fluids with electrolytes( like ORS, electoral , coconut water) if nothing available then simple lemon water with salt & sugar will work along with home made easy digestable food