If you are temporarily in Europe and still are able to use a U.S. checking or savings account, you might consider asking the Church to change your donation account so that you can donate from that U.S. account. You will then be able to contribute online directly to the missionary account of the ward in Colorado.
If you do this, you will no longer be able to donate online to a church unit in Europe.
If you need to continue donations in Europe, you might consider a divide and conquer approach. One of you could donate from a U.S. account and the other could continue to donate from a European account.
To do either of these options, you would send an email to
onlinedonationsupport@churchofjesuschrist.org and explain your situation, asking them to change your Church Account to allow you to donate from a U.S. bank.
Although more complicated, this approach will allow others in the U.S. to also contribute to that ward missionary account. If you transfer missionary financial responsibility to Europe, contributions from others become much more difficult.