They can if there is community property involved. At first, all of your assets will be separate, but over time, if you pay things together, the assets will become community property and the burden will be on you to show that they are not. They cannot just put a lien on her property the day you get married. But they could show up a year or two later claiming everything is community property, and making you prove it isn't. Keep good track of who pays for what and keep your expenses separate if you even intend to do this. A prenup can be used as well, but these have legal effect long after the tax debt is gone, and this is something only an experienced attorney should walk you through.
Another thing to consider, is in a community property state, half of her income is your property, and half of yours is hers. If she makes significantly more than you, you can almost bet that in the absence of a prenup, she will end up paying something toward your debt because her income will be included in the calculation to determine your means to pay the IRS.
Yes, the IRS can place a lien on property that is in her name, or in both your names, if they believe it to be community property, because they can collect from your property, and yours and her share of community property, including her income. You should consider a prenuptial agreement prior to marriage, or if already married a post nuptial agreement, which will at least protect her property, including her income, from the IRS collecting your taxes from her.
This information is provided for educational purposes only, and is not to be relied upon as legal advice. You should consult with an attorney with full disclosure of all facts and opportunity to consider all or alternative options.
If you get married, the tax lien will attach to your interest in any community property. The tax lien will not attach to any of the property your fiancee owns before marriage, except for any property that becomes community property because of the marriage.
If you and your fiancee, once you marry, acquire anything that becomes community property, then your tax lien will attach to your interest in that community property. This can reach further than one might think: for example, if your spouse's income is community property, the IRS can technically levy on your spouse's wages to collect on your taxes. This would be a one-time levy, not a continuous levy (i.e., a garnishment), but it would play havoc with things if it happened.
The best way to manage this situation is to (a) make sure you never default on your payment agreement, and (b) once you're married, if your then spouse acquires anything of substantial value, make sure you follow whatever steps are required to make sure it stays her separate property and doesn't become community property.
The most important thing is staying current with your installment payment plan. As long as you stay current with that, the IRS will not attempt any new enforced collection activities.
Finally, although the lien against you attaches to your interest in community property, the IRS as a matter of prudent policy will not file a new notice of federal tax lien against your fiancee, which means that your tax problems should not affect her credit ratings so long as you stay current on your installment plan. Her interest in any community property would be at risk from your tax lien, so a prudent buyer or lender to your fiancee may ask that for additional protection, but a credit card company will almost certainly not deny her credit because of your tax lien, again, so long as you remain current on your payment plan.
The bottom line is this: you and your fiancee should consult with a competent local family law attorney to make sure that your situation gets a thorough review and you get advice on any planning arrangements you need to consider.
The IRS has a little more detailed information in section 25.18.4 of the Internal Revenue Manual: http://www.irs.gov/irm/part25/irm_25-018-004.html#d0e78
My answer does not constitute legal advice and may not be relied upon by anyone for any purpose and does not constitute an attorney/client relationship or an offer to form such a relationship. This disclaimer is intended to be fully compliant with the requirements of Treasury Department Circular 230 and the terms thereof are fully incorporated by reference. If you wish to consult with me please contact me at dwatchley@newyorktaxcounsel or visit my website at www.newyorktaxcounsel.com