Maybe this is just me, but why even lie to this person? Making up some type of excuse just to pretend to be polite, really rubs me the wrong way.

Sorry, I don't lend patterns or sewing supplies. Would be what I would say. I would not offer any other explanation or excuse. Them there's the facts.

I only lend what I can afford to lose or no longer need.

I guess I feel differently about my patterns, I do not mind loaning them out, especially to a coworker who I see all the time and am pretty sure it will be returned. Things (patterns included) to me are to be used, shared, loved, enjoyed. When I began sewing and quilting if people I knew didn't share with me I wouldnt have been able to do all I have, and i try to pass it on.

Saying no is a bit harsh, considering you work with this person. I willingly share my patterns with my close friends who I know will return them in good condition and I don't mind a bit. I would not share with just a co-worker or acquaintance. I would just say that I am still using it and continue to use it for a long time, she will get the message. I would give her the information of how to get it anyway. Some people don't have a clue and I don't like to be too harsh unless they get obnoxious.

I have loaned patterns - some were gone for good, others were returned with no problems. For me, I would say that I was planning to make another item and give her the information about the pattern so she could either find it on her own or not. Sometimes I will ask someone where they got the pattern or the name and they act like I am going to make the identical thing. Chances are, I won't even make it, I like to know where other people shop for such interesting items.
Once on the QB I asked a person where she got an embroidery design for a major university, her response was very defensive saying she couldn't send the design to me. I didn't want the one she had I was hoping to find another university and had not been able to locate any so thought she had an avenue that I was not aware.

So don't get super defensive, it can create hard feelings, and you don't want to do that.

Wide variety of answers here! Made me think of things I had not even considered before. What I have said when some one has asked to borrow a pattern is that I didn't really use a pattern. I usually tweek or change something, or make my own, so them using the "pattern" won't get them the same quilt or wall hanging I made.

If it were one of my friends or co-workers, I would not mind letting someone borrow the pattern. I would feel flattered that they liked what I made. I would hope that they would be responsible enough to take care of the pattern and return it in a timely fashion. But if you want to borrow my scissors or rulers, I would think twice. Those things tend to be a bit more expensive than patterns.