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I'm considering getting a companion dog for my 10 month old female GSD to keep company with.  Would an older lab be an OK fit for that?

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All 4 of my females get along just fine. 2 Labs, 1 GSD, and 1 French Bulldog.

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All 4 of my females get along just fine. 2 Labs, 1 GSD, and 1 French Bulldog.

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I don’t have a whole lot of experience with multiple female dogs but I’ve never seen issues either. ?????

Two female dogs thrust together often cannot establish a stable pack order. And believe it or not, females are more likely to fight to the death than males are.

When two females are close in age, there is often a lot of competition. They will fight over several competing elements. Such fights seem to occur the most in the presence of the owner. They may fight over who walks first up a ramp of stairs or through the door, they may fight over sleeping areas, foods, treats and toys. Sometimes a cause may not be completely visible in the owner's eyes but it any case one dog may have felt challenged by the other dog and felt the need to send her back down the ladder.

Adopting a female younger dog when owning already a female senior dog as mentioned above is also high risk. The newer dog may perceive that the older dog as weak either because of sickness or weakness and may try to take over. Unfortunately, it's not unheard of such fights having a sad ending.

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While I have also had two female dogs placed together successfully, it is a commonly known possible problem.  That is why I said “Two female dogs can be problematic.”

I have also had to put a dog down because of aggressive behavior that could have been aggravated by the two female situation (although she became very aggressive with a male also).

Some information:
https://healthypets.mercola.com/sites/healthypets/archive/2013/12/04/two-dog-household.aspx

Some additional information:
https://pethelpful.com/dogs/The-Risks-of-Raising-Two-Female-Dogs