I claimed my daughter (19) as a dependent and used my income for her schooling even though she was away at school. But her dad wants to claim her on his his 2018 taxes.

[tanoshii]

She just switched schools and started living with her dad and his parts in October 2018. 

[Hal_Al]

if she live with you for more than half the year, you still have first choice on claiming her. This assumes she was a full time student for parts of 5 months.
Even if she wasn't it depends on more details

[tanoshii]

She went to school in Nevada as a full time and has been there up till October when she transferred to CA.  

[Hal_Al]

If she was living with you before she went to NV, and only went to NV for purposes of school, her time in NV is considered a temporary absence from your home, So,  she is considered to still be living with you, during that time.

[Hal_Al · Accepted solution]

A child of a taxpayer can still be a “Qualifying Child” (QC) dependent, regardless of his/her income, if:

1. He is under age 19, or under 24 if a full time student for at least 5 months of the year, or is totally & permanently disabled

2. He did not provide more than 1/2 his own support. Scholarships are considered third party support and not as support provided by the student.

3. He lived with the parent (including temporary absences such as away at school) for more than half the year

If she is your QC, the dad cannot claim her without your permission. 

Whoever does claim her also claims the tuition credit, regardless of who paid the tuition.