If I claim my adult daughter as a dependent (she lives with us and is unemployed) will it affect her own tax return?

First you need to see if she really meets the criteria to be claimed as your dependent.   Living with you is not enough.   If she is older than 23 and had at least $4300 of income (not counting Social Security) you cannot claim her as a dependent.   Being claimed as a dependent will prevent her from getting a stimulus check---so you need to be really sure before you claim her.

IRS interview to help determine who can be claimed:

https://www.irs.gov/help/ita/who-can-i-claim-as-a-dependent

Does she fit the criteria to be your qualifying chid or your qualifying relative?

WHO CAN I CLAIM AS A DEPENDENT?

You can claim a child, relative, friend, fiance (etc.) as a dependent on your 2019 taxes as long as they meet the following requirements:

Qualifying child

• They are related to you.

• They cannot be claimed as a dependent by someone else.

• They are a U.S. citizen, resident alien, national, or a Canadian or   Mexican resident.

• They are not filing a joint return with their spouse.

• They are under the age of 19 (or 24 for full-time students).

• No age limit for permanently and totally disabled children

  •      They live with you for more than half the year (exceptions apply).

Qualifying relative

• They don't have to be related to you (despite the name).

• They cannot be claimed as a dependent by someone else.

• They are a U.S. citizen, resident alien, national, or a Canadian or Mexican resident.

• They are not filing a joint return with their spouse.

• They lived with you the entire year.

• They made less than $4300  (not counting Social Security)

• You provided more than half of their financial support. More info

When you add someone as a dependent, we'll ask a series of questions to make sure you can claim them.

Related Information:

• Does a dependent have to live with me?

• What does "financially support another person" mean?

• Can I claim a newborn baby?