there are several things used to compute the credit. for the initial maximum credit both spouses must contribute. line 6 for each column would then be $2000 line 7 would be $4000. with an AGI of around $39,000, 50% of line 7 is initially allowed as a credit on line 10 ($2000).  for one contributor lines 6 and 7 would be $2,000 and with the same AGI then line 10 would be $1,000.  then there is line 11 which limits the credit based on tax liability.  

so you are correct since only she makes a contribution.  $1,000 credit with an AGI of around $39K, possibly limited by line 11. 

"It seems a bit unfair".  there are many provisions of the code that one could deem unfair - that favor some taxpayers over others.

Q. Does the Retirement Savers Credit need both spouses to be contributing to a plan to get the maximum credit?

A.  Yes.

Q. I've been having difficulty tracking down exactly how the Retirement Savers Credit  works for Married Filing Jointly filers.

A. Follow the steps (lines) on form 8880.   https://www.irs.gov/pub/irs-pdf/f8880.pdf There are two columns, one for each spouse.  The 2nd spouse does not get to use the 1st spouse's contributions.

Q. I've read that married filing jointly filers get a maximum. But Form 8880 makes it look like that is per filer.

A.  You read wrong.  It is "per filer", or more specifically per retirement plan contributor. 

Q.  It seems a bit unfair to families that focus on maxing out one person's retirement account. 

A. Not really. The credit is for individuals saving for retirement, not families.  

Note for others reading this: poster refers to "getting a maximum $2000 credit".  That amount is for his AGI and the maximum qualifying  contribution amount of $4000 ($2000 per spouse).  See the table on  form 8880 for credit calculations.