Would the answer be the same whether the IRA or the IRA's LLC was the purchaser? 

Yes, long term money (IRA) money is great for participating in syndication deals as a limited partner because of self interest rules in not being active w/your own IRA money.  

I do not recommend the Ira owner be the manager of their Ira LLC. 

@Austin TalbertThere are a number of specialty firms that provide services around investing tax-sheltered IRA or 401(k) money into alternative assets like notes, real estate, etc.The big firms focus on what they do, which is publicly traded assets like stocks and funds.  

Is it better to withdraw her IRA/401K (and pay taxes) OR to convert the IRA to a self-directed IRA (SDIRA) to purchase a rental property.

For example, I am planning to invest in REI using my self direct 401k or IRA, but I can't self deal, so I would probably invest in somebody else project down the road. 

Many members are experts in their respective fields related to real estate investing, whether that is real estate brokerage, wholesaling, flipping, buy and hold, lending, self-directed IRA and Solo 401k investing, or tax and legal guidance.There are some pretty cool discounts on various products and services offered as Perks to BP members that you might want to check out: https://www.biggerpockets.com/perks/pro

We’re leaning towards a HELOC and could also tap other accounts like 401k, IRA, etc.

A lot of forum members are very knowledgeable in their respective fields related to real estate investing, whether that is real estate sales, wholesaling, flipping, rentals, lending, self-directed IRA and Solo 401k investing, or tax and legal guidance.Discounts on some products and services are offered to BP members: https://www.biggerpockets.com/perks/proIf you haven’t been to it already, you might want to check out the BP blog: https://www.biggerpockets.com/blog/The site has quite a few tools that can be helpful for new members.

My wife and I are currently not maximizing our Roth IRAs in order to save up.