But,It really shouldn't be that hard to add/drop properties to an umbrella policy. 

How should that protection be modified as you start to add multiple properties to your portfolio (umbrella policies/etc.)? 

LLC is best for asset protection.you could use a trust which helps hide ownership but doesn't give you any protection.You could just keep in your name with a mortgage and insurance on each property and an umbrella policy.

You’ll still need to buy the same insurance and maybe umbrella policy.

What is the appropriate amount of Umbrella coverage does one need to ensure adequate/robust (but not excessive) coverage? 

My rule of thumb -If net wealth < $1M, then $2M umbrella policyIf net wealth > $2M, then $2M umbrella policy and LLC. 

We where under the impression that the LLC was more of a benefit incase something was to happen to protect us, she advised us to get  more coverage on our insurance policy or umbrella coverage.

Do not use your personal account.Carry $300,000 liability insurance on each rental and a $1 million umbrella policy.

Should I purchase those so I can move them under the LLC umbrella or leave them in her name ?

Landlord insurance and or umbrella as well.