Real Estate Agents only get paid when they sell something.
Remember you do not pay the commission, the seller does. I would think it fair on your part if you had a talk with the agent, I'm sure he or she would do the work for both seller and buyer while dropping the commission to something you could live with. Please be fair.
Are you and the members of the selling family ready to not speak to each other ever again?
Good luck with the transaction with your relative! These transactions can often be more difficult to handle than purchasing from a stranger. Even if she released you from the agreement, I recommend you keep her phone number handy.
If you trust your agent and would rather they just represent you, then consider that the commission will be well worth it and it can be possibly worked into the offer. 3% is a typical buyer agent commission so just work it into the offer or try to get your relative to help you out with 1/2 (1.5%).
If its really so cut and dry that you know an agent isn't needed, then try to do it privately, but I would not recommend this as it is never cut and dry these days and especially with relatives if things get ugly. You may wish you had a in-between for this. There are many different ways a buyers agent can get paid. It not necessarily going to be cash right out of your pccket at closing. Research before you make your decision.